Unity magnification symmetrical lens system

ABSTRACT

A unity magnification lens system of focal length F comprises a symmetrical pair of similar telephoto lens systems and includes 12 lenses, the sixth and seventh lenses being singlets or doublets and the remaining lenses being singlets, the first, fifth, eighth and twelfth lenses being negative and the rest positive. The absolute value of each lens face radius of curvature exceeds 0.7F and of each positive lens exposed face exceeds F, the index of refraction of each positive lens exceeds 1.65, and the rear face of the first lens and the front face of the twelfth lens are concave with absolute radii of curvature between 0.7F and 1.5F.

United States Inventors Toliru Matsulnoto UNITY MAGNIFICATIONSYMMETRICAL LENS SYSTEM 4Clalms,5DrawingFlga.

US. Cl. 350/214 lnLCl. G02b9/64 Field ofSearch 350/2l5, 216,214, 175TS,2l2

TEL/09) Primary Examiner-John K. Corbin Attorney- Stanley WolderABSTRACT: A unity magnification lens system of focal length F comprisesa symmetrical pair of similar telephoto lens systems and includes l2lenses. the sixth and seventh lenses being singlets or doublets and theremaining lenses being singlets, the first. fifth, eighth and twelfthlenses being negative and the rest positive. The absolute value of eachlens face radius of curvature exceeds 0.7F and of each positive lens exposed face exceeds F, the index of refraction of each positive lensexceeds L65, and the rear face of the first lens and the front face ofthe twelfth lens are concave with absolute radii of curvature between0.7F and LSF.

PATENTEnncI 19ml 3.614.208 SHEET 10F 2 INVENTOR TOHRU MATSUMOTO BY MUMATTORNEY PAIENIEDnm 19 ISII SHEEI 2 0F 2 I9.6 mm

-0.l +0.I -0.00l +0.00! SPHERICAL ABERRATION DISTORTION AND SINECONDITION l=25 39.6mm

I9.7 mm

-Q| +0.l -0.00| +0.00! SPHERICAL ABERRATION DISI'ORTION AND SINECONDITION ASTIGMATISM (BROKEN LIIE: MERIDIONAL SOLID LINE= SAGITTAL I39.6 mm

2 l9] mm I ASTIGMATISM BROKEN LINE: MERIDIONAL) SOLID LINE= SAGITTALINVENTOR TOHRU MATSUMOTO ATTORNEY BACKGROUND OF THEINVENTION The presentinvention relates generally to improvements in lens systems and itrelates particularly to an improved unity magnification lens system.

A conventional wide-angle objective lens system with small distortionaberration, as typified by the Zeiss Viogon objective, is characterizedby a pair of similar telephoto lens systems symmetrically positionedrelative to a medially axially located diaphragm. As seen in FIG. I ofthe drawings, hereinafter identified, the double telephoto lens systemof the present invention generally includes a front telephoto lenssystem including a front outer negative lens group R, followed by aspaced inner second positive lens group R, positioned at the front orobject side of a diaphragm F and a second telephoto lens systempositioned at the rear on the image side of diaphragm F and includes afront inner positive lens group R, followed by a spaced outer fourthnegative lens group R lens groups R and R,- defining a first telephotolens system and R, and R, defining a second telephoto lens systemsimilar to and symmetrical relative the first telephoto lens system. Theconventional double telephoto wide angle objective lens system possessesnumerous drawbacks and disadvantages. It possesses relatively highSeidels coefficients and significant aberration values and otherwiseleaves something to be desired.

SUMMARY OF THE INVENTION It is a principal object of the presentinvention to provide an improved lens system.

Another object of the present invention is to provide an improved highlycorrected wide-angle objective lens system.

Still another object of the present invention is to provide an improvedlens system of the symmetrical double telephoto lens type.

A further object of the present invention is'to provide an improved lenssystem of the above nature characterized by very low Seidel scoefficients and very low aberration.

The above and other objectives of the present invention will becomeapparent from a reading of the following description taken inconjunction with the accompanying drawings which illustrate preferredembodiments thereof.

In a sense the present invention contemplates the provision of asubstantially unity magnification lens system of overall focal length Fcomprising a symmetrical pair of front and rear substantially similartelephoto lens systems each including a negative outer lens group and apositive inner lens group and characterized in that:

a. the absolute value of the radius of curvature of each lens face isgreater than 0.7F;

b. the absolute value of the radius of curvature of the exposed lensfaces of each lens is greater than F;

c. The index of refraction of each positive lens is greater than 1.65;

d. the rear inner lens group includes a negative lens and the lenses areso related and dimensioned that rays parallel to the optical axisbetween said telephoto lens systems issue from said negative lens asdiverging rays;

e. the rear outer and inner lens groups are spaced to form a telephotoobjective lens system; and

f. said rear outer lens group comprises a rear negative lens with aconcave front face of absolute radius of curvature between 0.7F and LSF.

To great advantage the improved lens system includes 12 successivelenses symmetrically arranged on opposite sides of a medially axiallylocated diaphragm. The first and 12th lenses are negative lenses withinwardly facing concave faces of greater curvature than their outsidefaces, and the fifth and eighth lenses are double concave lenses, theremaining lenses being positive lenses. All of the lenses are singleelement lenses except for the sixth and seventh lenses which may besingle element lenses or doublets with cemented surfaces.

In the present lens system, the rays which issue from a point on theoptical axis are caused to sharply diverge by the negative first lens Iof the front lens group. Then, after passing through the second lens 2through the sixth lens 6 of the posi: tive lens group, said rays passthrough the diaphragm F as rays which are parallel with the opticalaxis. These parallel rays pass through the rear lens groups, namely theseventh lens 7 through the twelfth lens 12, and form a unitymagnification image.

In order to obtain such a lens system of high quality, it is necessaryto make the Petzval sum smaller than in the case of an ordinaryobjective, and also to make the spherical aberration small. Seidel'scoma tenn is made small through the law of symmetry, but, actually, toremove coma aberration is very difficult. Distortion aberration isremoved through the law of symmetry almost satisfactorily.

It has been found that to obtain a unity magnification objective of thesubject type in which the aberrations are highly compensated, it isnecessary to satisfy the above six conditions (a) to (f). Theconditions-(a) and (b) function to minimize spherical aberration andcoma aberration. In conventional lens systems, however, with suchconditions only it is difficult to eliminate curvature of image field.In the lens system of the present invention, the provision of thefurther conditions (c), (d) and (e) serves to reduce the Petzval sum.

Condition (f), the concave front face of the rear-most negative lensbeing made. largerthan 0.7F, is necessary for reducing the comaaberration caused by this surface. Since this surface serves also forcompensating astigmatism, too large a value of the radius of curvaturewould make the astigmatism compensation difficult, and for thiscompensation it would be necessary to have a greater curvature of thesecond surface of the second lens, which would inevitably result inaggravation of coma aberration. For such reason, it is necessary to havea radius of curvature which is smaller than 1.5 F.

The improved lens system: is of substantially unit magnification and ischaracterized by very low Seidel's coefficients and very low aberration.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic diagramgenerally illustrating the principal of a lens system according to thepresent invention;

FIG. 2 is a longitudinal sectional view of a preferred embodiment of thepresent invention;

confronting mating FIG. 3 is a longitudinal sectional view of anotherembodiment of the present invention;

FIG. 4 are graphs of the aberration characteristics of the lens systemof FIG. 2; and

FIG. 5 are graphs of the aberration characteristics of the lens systemof FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingsand particularly FIG. 2 thereof which illustrates a preferred embodimentof the present invention, the improved lens system comprises 12 lensesconsecutively designated as the first to the twelfth lens, the first tothe sixth lens constitute a first telephoto lens system and the seventhto the twelfth lens constitutes a second telephoto lens system similarto the first telephoto lens system and symmetrical thereto relative to adiaphragm F located between the sixth and seventh lens. The first lens 1defines the first lens group as identified above and is negative with aconvex outer or front face and a concave rear or inner face of greatercurvature than the outer face and the twelfth lens 12 defines the fourthlens group and is similar and symmetrical to lens 1 with a convex rearouter face and a concave front or inner face of greater curvature thanthe outer face. The second to sixth lenses and the seventh to eleventhlens define the second and third groups respectively, the second andthird groups including similar lenses symmetrical relative to diaphragmF. The second lens 2, fourth lens 4, sixth lens 6, seventh lens 7, ninthlens 9 and eleventh lens 11 are positive double convexlenses and thethird lens and tenth lens 10 are positive meniscus lenses with convexouter faces.

The lens faces are successively consecutively identified as the first tothe twenty-fourth from the front face of lens 1 to the rear face of lens12 and r, designates the radius of curvature of the ith lens face, thatis the front and rear faces of lens 1 are designated r, and r,respectively, of lens 2, r; and r, and of lens 12, r and r The axialdistance between the ith lens face and the next successive or i+l lensface is designated as d1; 61,, d,, d, d designating the thicknesses oflenses 1, 2. 3 12 respectively, and d,, d,, d, d designating the spacingbetween lenses 1 and 2, 2 and 3, 3 and 4 11 and 12 respectively.

The following example I sets forth the specific values and relationshipsof a lens system of FIG. 2, by way of illustration, the lens systemhaving a brightness value of 1:25, a numerical aperture value of 0. l ,f=f,,:=97.78, F=l02.6, and e-line compensation up to d-line, n, and Vbeing the index of refraction and Abbe 3 number of the nth lens:

EXAMPLEI R D N, v,

The following table I sets forth the Seidel's terms for e-linecompensation in example lwherein S, denotes spherical aberration, S,coma aberration, S, astigmatism, P Petzval term and S, distortionaberration:

TABLE 1 Seidels Terms of e=line Compensation) S, S, S, P S,

TABLE l-Continued (Seidels Terms of e-line Compensation) FIG. 4illustrates the curves for spherical aberration and sine condition,distortion and astigmatism for the lens system of example 1.

In FIG. 3 of the drawings there is shown another embodiment of thepresent invention which differs from that shown in FIG. 2 only in thatdoublets are substituted for the single element lens 6 and 7 of the FIG.2 embodiment. Specifically, in place of lens 6 a doublet including anegative meniscus front element 6A with a concave rear surface and adouble convex rear element 68, the confronting faces of elements 6A and68 being cemented and mating and defining a single lens face. Similarly,lens 7 is substituted by a cemented rear doublet symmetrical to thefront doublet and including a front double convex positive element 7Aand a rear negative element 7B corresponding to elements 68 and 6Arespectively, the ce-v mented surfaces defining a single lens face. Thefourth and ninth lenses are positive meniscus lenses with convex outerfaces and in all other respects the embodiments shown in F 16$. 2 and 3are similar.

The lens faces are successively designated with the cemented elementsurfaces defining a single lens face, r, being the radius of curvatureof the ith lens face and d, being the axial distance between the ithlens face and the next successive lens face.

The following example 11 sets forth the specific values andrelationships of a lens system shown in FIG. 3, the lens system having abrightness value of 1:2.5, a numerical aperture value of 0.1,F=l08.2,f,=f,,'=l 12.63, and g-line compensation up to the Mine:

EXAMPLE [I R 1) N, v,

1, 702.530 6, 14.09 11, -1.52619 64.1 1, 90.467 6, =59.17 1, 931.347 6,=14.09 11, l.7l060 50.7 1, 351.430 6, 9.02 1, 240.236 6, -14.09 11,1.71060 50.7 1, 1644629 6. 0.56 1, 267.123 6, -14.09 11, -1.7770735.0 1. 925.130 6,. -11.z7 '1, 152.079 6, 13.74 11, 1.74917 29.5

The following table 11 sets forth the Seidel's terms for g-linecompensation in example 11:

TABLE 11 1 0.054 0.079 0.116 0.053 0.248 2 0.769 0.250 --0.081 0.4120.160 3 0.487 0.250 0.129 0.045 0.090 4 0.008 0.0- 0. 195 0.127 0.329 50.501 0.244 0.119 0.187 0.149 6 0.012 0.036 0.106 -0.027 0.389 7 0.1190.121 0.123 0.177 0.305 8 0.000 0.000 0.002 0.051 -0.544 9 0.173 0.224"-0.289 0.304 0.766 10 -2.660 1.054 "0.417 0.236 0.259 11 1.874 0.9220.453 0.143 0.293 12 0.426 0.079 0.014 0.017 0.0% 13 0.174 -0.165 0.1570.279 0.414 14 0.174 0.169 0.165 0.279 0.433 15 0.426 "0.068 0.011 0.017"0004 16 1.874 "0.877 0.410 0.143 0.258 17 2.660 0.989 0.368 0.Z36 0.22518 0.173 0.2Z8 -0.300 0.304 "0.795 19 0.000 0.000 0.002 -0.051 0.542 200.119 0.118 0.117 0.177 0.292 21 0.012 0.036 0.105 0.027 0.381 22 0.5010.232 0.108 0.187 "0.136 23 0.008 0.039 "0.193 0.127 0.318 24 0.487 0.230.117 0.045 0.079 25 0.769 0.269 0.094 0.412 -0.177 26 0.054 "0.0780.112 0.053 -0.238 SUM 0.026 0.000 0.008 "0.001 0.1110

FIG. 5 illustrates the curves for spherical aberration and sinecondition, distortion and astigmatism for the lens system ofexample lI.

As seen in tables I and [I the sums of each of the Seidel's terms arevery small. Moreover, the curves illustrated in FIGS. 4 and 5demonstrate that in both e-line and g-line compensation in the presentimproved lens system, the aberrations up to i 39.6 mm. image extensionare excellently compensated. It should be noted that since the raystraversing diaphragm F are parallel to the lens system optical axis, anoptical filter may be positioned anywhere between the lenses 6 and 7 orlens elements 6B and 7A without effecting the aberration conditions ofthe lens system.

While there have been described and illustrated preferred embodiments ofthe present invention, it is apparent that numerous alterationsomissions and additions may be made without departing from the spiritthereof.

What is claimed is:

1. A substantially unity magnification lens system comprising 12consecutively designated lenses including a symmetrical pair of frontand rear substantially similar telephoto lens system eachincluding anegative outer lens group and a positive inner lens group in which thefirst lens is negative with a concave rear face, the second lens ispositive with a convex rear face, the third lens is positive with aconvex front face, the fourth lens is positive with a convex front face,the fifth and eight lenses are doubly concave, the sixth and seventhlenses are doubly convex, the ninth lens is positive with a convex rearface, the tenth lens is positive with a convex rear face, the eleventhlens is positive with a convex front face, and the twelfth lens isnegative with a concave front face.

2. The lens system of claim 1 wherein said sixth lens is a doubletincluding a negative front lens element with a concave rear surface anda double convex rear lens element and said seventhlens is a doubletincluding a double convex front lens element and a negative rear lenselement with a concave front 6 surface.

3. The lens system of claim 1 comprising l2 consecutively designatedsingle element lenses having 24 consecutively designated lens faces andpossessing the following dimensions and relationships:

r,. 279.s22 d 111.74 11, 1.64419 34.6 1., 99.030 d... 1127 designatedlenses, the sixth and seventh lenses being doublets with single lensface defining cemented confronting mating surfaces, the lens elements ofsaid doublets being consecutively designated as 6A, 68, 7A, and 73respectively, the remaining lenses being single element lenses, saidlenses possessing the following dimensions and relationships:

wherein r, is the radius of curvature of the ith lens face, :1, is theaxial distance between the ith lens face and the 1+1 lens face, and n.is the index of refraction of the nth lens.

1. A substantially unity magnification lens system comprising 12consecutively designated lenses including a symmetrical pair of frontand rear substantially similar telephoto lens system each including anegative outer lens group and a positive inner lens group in which thefirst lens is negative with a concave rear face, the second lens ispositive with a convex rear face, the third lens is positive with aconvex front face, the fourth lens is positive with a convex front face,the fifth and eight lenses are doubly concave, the sixth and seventhlenses are doubly convex, the ninth lens is positive with a convex rearface, the tenth lens is positive with a convex rear face, the eleventhlens is positive with a convex front face, and the twelfth lens isnegative with a concave front face.
 2. The lens system of claim 1wherein said sixth lens is a doublet including a negative front lenselement with a concave rear surface and a double convex rear lenselement and said seventh lens is a doublet including a double convexfront lens element and a negative rear lens element with a concave frontsurface.
 3. The lens system of claim 1 comprising 12 consecutivelydesignated single element lenses having 24 consecutively designated lensfaces and possessing the following dimensions and relationships: r1733.498d1 14.09 n1 1.5848340.8r2 107.246d2 70.44r3 1722.209d3 14.09 n21.7323554.8r4 -398.531d4 9.02r5 425.155d5 14.09 n3 1.7323554.8 r6-867.243d6 0.56r7 568.460d7 14.09 n4 1.7323554.8r8 -896.762d8 11.27r9-99.030d9 18.74 n5 1.6441934.6r10 279.822d10 1.41 r11 296.460d11 28.17n6 1.7323554.8r12 -146.748 d12 10.40 r13 146.748d13 28.17 n7 1.7323554.8r14 -296.460d14 1.41 r15 -279.822d15 18.74n8 1.6441934.6r16 99.030d1611.27r17 896.762d17 14.09 n9 1.7323554.8r18 -568.460d18 0.56r19867.243d19 14.09 n10 1.7323554.8r20 -425.155d20 9.02r21 398.531d21 14.09n11 1.7323554.8r22 -1722.209d22 70.44 r23 -107.246d23 14.09 n121.5848340.8r24 -733.498 wherein ri is the radius of curvature of the ithlens face, di is the axial distance between the ith lens face and the i+1 lens face, and nn is the index of refraction of the nth lens.
 4. Thelens system of claim 1 comprising 12 consecutively designated lenses,the sixth and seventh lenses being doublets with single lens facedefining cemented confronting mating surfaces, the lens elements of saiddoublets being consecutively designated as 6A, 6B, 7A, and 7Brespectively, the remaining lenses being single element lenses, saidlenses possessing the following dimensions and relationships: r1702.530d1 14.09n1 1.5261964.1r2 90.467d2 59.17r3 981.847d3 14.09n21.7106050.7r4 -351.480d4 9.02 r5 240.286d5 14.09n3 1.71060 50.7 r61644.629d6 0.56r7 267.123d7 14.09n4 1.77707 35.0r8 925.180d8 11.27r9-152.079d9 18.74n5 1.7491729.5 r10 195.727 d10 4.23r11 322.505 d118.45n6A 1.7456654.8r12 92.741d12 19.72n6B 1.7933049.2 r13 -171.138d135.68r14 171.138d14 19.72n7A 1.7933049.2 r14 -92.741d15 8.45n7B1.7456654.8 r16 -322.505d16 4.23r17 -195.727d17 18.74n8 1.7491729.5 r18152.079d18 11.27 r19 -925.180d19 14.09n9 1.7770735.0 r20 -267.123d200.56r21 -1644.629d21 14.09n10 1.7106050.7 r22 -240.286d22 9.02r23351.480d23 14.09n11 1.7106050.7r24 -981.847d24 59.17r25 -90.467d2514.09n12 1.5261964.1r26 -702.530 wherein ri is the radius of curvatureof the ith lens face, di is the axial distance between the ith lens faceand the i+1 lens face, and nn is the index of refraction of the nthlens.